1. Field of the Invention
The present invention relates to an image forming apparatus, and more specifically relates to a full-color image forming apparatus.
2. Description of the Related Arts
Digital full-color image forming apparatus which form full-color images based on digital image data using cyan, magenta and yellow color toners have been known for some time.
Full-color image forming apparatus also have been proposed wherein the picture portion and the character portion of the original document are discriminated. The picture portion of the original document is subjected to image formation by multicolor overlays of color toners, while the character portion is subjected to image formation by a single color toner such as black toner or the like so as to avoid a reduction in image quality in the character portion thereof and maintain the fidelity of the reproduction of the color display of the image portion thereof.
Color image forming apparatus are also known which employ an under color removal (UCR) process wherein the black regions and shadow regions of the image portion are removed from the three-color toner developing and developed with black toner in a substitution process so as to enhance image registration and improve line reproducibility as well as reduce the consumption of color toner.
However, when the picture portion is developed by multicolor overlays of color toners and the character portion is developed by a black toner, there is a disadvantage in that the character portion is developed under developing conditions that optimize the color reproducibility in the image portion, thereby detracting from the reproducibility of the character portion. Conversely, when developing conditions are set to optimize the reproducibility of the character portion, the color reproducibility of halftones in the picture portion is reduced.
These disadvantages also occur in the image forming apparatus using the previously mentioned UCR process.